When you requested your hearing, you (or your attorney) should have also requested a stay on the suspension. The DMV would have then sent you notice that the suspension that was due to kick in after 30 days from your arrest was put on hold until the outcome of your hearing.
If you lose your hearing, the DMV will issue their ruling in writing within 2 weeks of the hearing and notify you of the effective date of the suspension. No, it can't be retroactive.
I agree with Attorney J. Dane. I also want to point out, though, that some DMV offices are backlogged and are not very prompt about evaluating the evidence at a hearing and subsequently notifying the drivers of the hearing results. The Van Nuys Driver Safety Office, for example, is notoriously backlogged and it might be months before a decision on your hearing is made or conveyed. Furthermore, although suspensions cannot be retroactive in the strict sense of the word, it is possible to get credit against your suspension if your attorney can prove to the DMV hearing officer that you have not been driving despite the stay on your license suspension.
Good advice from both the other lawyers here. However, something tells me you don't have a lawyer representing you. I say this because of the timing of your hearing and 30-day temporary are so close in time. You couldn't have been arrested more than 3 weeks ago since you still have the 30-day temporary and you have a hearing in just a week or so. My guess is that your hearing is telephonic since no DMV office could have scheduled an in-person hearing that quickly.
My suggestion is that you get an attorney and have him/her represent you at the hearing and at court where you probably haven't been arraigned yet. The attorney can most likely get a continuance of your hearing at the DMV and extend your driving for a considerable period of time; the attorney can also review your police report and other evidence against you which you may not now have.
If you are representing yourself at this DMV hearing you will not win and you will be suspended very quickly, regardless of the backlog at the DMV,